The present invention is generally related to the field of color printing and, more particularly, is related to a system and method for reducing horizontal banding and misregistration between color planes in a color image.
Color printing systems offer new printing capabilities that are changing the way documents are printed. In the past, color printing was only available through printing shops and other entities that could afford prior technologies to create color images. Now, color printers are available that bring color printing to the home of the average individual at reasonable cost. Various technologies are employed to generate color images including ink jet printers. Laser printing technology also offers a promising alternative to ink jet printers, although the current state of laser printing technology is not without problems.
The problems experienced with laser printing technology are related to the internal process of the laser printing technology itself. For example, a typical laser printer generates color images using four colors including cyan, yellow, magenta, and black (CYMK). In order to produce a specific color on a print medium such as, for example, the color purple, a predetermined number of CYMK spots are placed on the print medium next to each other. The print medium may be, for example, paper or other material. The size of each of the CYMK spots is so small that each individual spot is not perceived by the naked eye. That is to say, when viewed by the average individual, the combination of CYMK spots appears as a single color of purple. The many different colors in existence may be generated in this manner.
To place the CYMK spots next to each other, each individual color is placed on the print medium independently of the other colors in so called xe2x80x9ccolor planesxe2x80x9d. That is to say, each color plane includes all of the spots of one of the CYMK colors of a particular image. In current laser printers, each of the color planes is developed separately and ultimately applied to the print medium either directly or indirectly. At some point, the four color planes are brought together by sequentially placing each of the CYMK colors down on the print medium or on an image transfer belt so that they occupy the same image plane.
Unfortunately, it can be difficult to place each of the CYMK color planes on the same image plane with accurate positioning relative to each other. Specifically, there may be printer structural tolerances, velocity fluctuations, optical imperfections, gear train imperfections and other problems that prevent the various color planes from being placed in an image in perfect relationship to each other. This is generally referred to as misregistration of the color planes. However, the dots are generally accurately placed within the individual color planes relatively to each other.
There are several negative consequences that may result due to the misregistration of the color planes in an image. For example, the shifting of the color planes relative to each other often may result in an undesirable hue shift in the resulting colors. Also, undesirable moirxc3xa9 patterns and white gapping as well as other anomalies may appear in the resulting image that are apparent to the naked eye.
In light of the forgoing, the present invention provides for a system and method for generating a color plane in an image. According to the present invention, a noise generation device is coupled to at least one component within a laser imaging assembly to cause a random deviation in the placement of the spots within respective color planes. This random deviation advantageously alleviates the problem of misregistration, white gapping, and moirxc3xa9 patterns, etc.
According to one embodiment, a system is provided that includes a laser imaging assembly having a laser generating a laser beam that is optically coupled to a photoconductor, typically an organic photoconductive (OPC) drum. The laser beam is optically coupled to a number of predetermined positions on the photoconductor to generate an image on the photoconductor. A noise generator is operatively coupled, for example, to a component in the laser imaging assembly. The noise generator causes a random motion, for example, in the component, thereby generating a random deviation of each of the predetermined positions on the photoconductor to which the laser beam is optically coupled.
In addition, the present invention includes a method for generating a color plane in an image. The present method comprises the steps of optically coupling a laser beam from a laser to a number of predetermined positions on a photoconductor, and generating a random deviation of each of the predetermined positions.